The present invention refers to a pressure switch, and in particular to a pressure switch for high working pressure.
A conventional pressure switch includes a spring-loaded piston acted upon by a pressure fluid in opposition to the force of the spring for actuating a switching element (e.g. a microswitch) upon reaching a switch point which is preset by the spring. The piston is sealed from the pressure fluid by dynamic sealing elements such as lip seal rings, O-rings or like sealing elements. The use of such dynamic sealing elements is, however, disadvantageous as progressive wear inevitably causes leakage so that fluid will penetrate the interior space of the working parts of the switch. The provision of a drain bore to allow leaky fluid to be discharged into the open is not suitable in connection with pressure switches as this would compromise safety regulations with regard to explosion proofness thereof.
It was thus proposed, at least for pressure switches operating with smaller system pressures of up to about 50 bar, to use diaphragms which are generally made of elastomer material in order to separate the working parts of the pressure switch from the pressure fluid. At higher system pressures, such diaphragms behave almost like highly viscous liquids so that diaphragm material frequently creeps e.g. into the sealing gap between the piston and the piston guide to clog the sealing gap. This results in considerable friction and significant deviations of the switch point. For that reason, the use of pressure switches with diaphragms has been limited to relatively low system pressures.